Muppets - is this humor or an in-joke?

I was looking at this photo I took of the pin-up calendar at Muppetvision 3-D, and noticed something odd:

Just below Miss PIggy, someone wrote "June." However, the calendar is a July calendar. The fine print below the 4th says Independence Day and the 1st says Canada Day. (Click on the photo to see a larger version.)

Does anyone know if this has any special meaning, or if it's just a joke?

And in case you're wondering, the calendar is on the wall in the security guard's office just inside the attraction entrance.

As promised, I sent my query off the Shawn Slater. Sadly, there's no interesting story to tell:

"As for the Muppet*Vision 3-D detail you point out, it's actually the first time I've noticed that. Unfortunately, it looks like the word "JUNE" was pencilled in, probably by a vandal (either cast member or guest). The Imagineering designer most likely left the month off, so the detail would remain timeless. This sort of thing is done often, unless there's a specific reason to highlight a month or date (the fact that it's a July calendar page would have been considered irrelevant, since most observers wouldn't be looking that closely)."